1. Field of the Invention
The present invention relates to a polishing apparatus and a polishing method for polishing a substrate, such as a semiconductor wafer, and more particularly to a polishing apparatus and a polishing method for polishing or grinding a peripheral portion of a front or back surface of a semiconductor wafer in a process of manufacturing a semiconductor device.
2. Description of the Related Art
In polishing of a peripheral surface portion (edge portion and bevel portion) of, e.g., a semiconductor wafer by the use of a polishing tape having abrasive particles fixed on a surface, it is common practice to press the surface of the polishing tape against the peripheral surface portion of the semiconductor wafer, rotating in a horizontal plane, at a predetermined pressure while supplying pure water to the surface of the semiconductor wafer.
In a semiconductor wafer W as shown in FIG. 10, the “bevel portion” of a semiconductor wafer herein refers to a portion B consisting of an upper inclined portion P and a lower inclined portion Q of an upper surface and a lower surface, respectively, of the semiconductor wafer W, and a peripheral side surface portion R of the semiconductor wafer W. The “edge portion” of a semiconductor wafer herein refers to a portion E lying between a boundary of the bevel portion B and a device area D of the upper surface, in which semiconductor devices are formed, of the semiconductor wafer W as shown in FIG. 10.
A method for polishing a peripheral portion (edge portion and bevel portion) of a silicon substrate has been proposed. The method comprises pressing a polishing tape, e.g., having ceria abrasive particles fixed thereon, against the peripheral portion of the silicon substrate, rotating in a horizontal plane, while supplying pure water to the peripheral portion (polishing portion) of the silicon substrate, thereby polishing away an insulating film and exposing the underlying silicon, and thereafter polishing the silicon by using a polishing tape having diamond abrasive particles which have a higher silicon polishing ability than ceria abrasive particles (see Japanese Patent Laid-Open Publication No. 2008-263027).
The applicant has proposed a polishing apparatus which can polish a peripheral portion of a substrate, including a flat portion, with a polishing tape while maintaining the original angle of the peripheral portion (see Japanese Patent Laid-Open Publication No. 2009-208214).
It has recently been proposed to manufacture an SOI (silicon-on-insulator) substrate by a bonding method which involves bonding, through heat treatment, two silicon substrates: a device substrate having semiconductor devices, and a supporting substrate. In a known method for manufacturing an SOI substrate, a first silicon substrate (device substrate), having a surface semiconductor layer (SIO layer) and whose peripheral surface portion has been polished away, and a second silicon substrate (supporting substrate), facing each other, are bonded via an insulting film, and then the back side of the first silicon substrate (device substrate) is polished or etched away, leaving the semiconductor layer (see Japanese Patent Laid-Open Publication No. H4-85827).